Big waves, big wins and a big year for firsts, these are the greatest sporting moments of 2015.

Competitive? Listen to the banter between English sisters Caroline and 'Leo' Bowen and you'll know how competitive they are.

As they start chatting about their standings in the Clipper round the world race of which the 628 nautical mile Sydney to Hobart is the next and sixth of 14 legs, it doesn't take long for good natured rivalry to rise.

"I think we might be tied on points ...," Caroline, 35 and a strategy manager on land, says when her younger sister, Leo, 32 and a doctor, suddenly interjects.

"No ... Garmin is one point above ...," Leo says grinning in reference to the name of her boat Garmin which is third overall after four legs, while her elder sister's boat Qingdao is in fifth place on the standings.

"I think we both have competitive natures," Caroline says.

"The sailing we have done has always been racing but we have often been in difference fields. We have been in different classes of boats.

"We have gone in different paths in life, so have not had to be in direct competition. "This is a bit of an unusual situation where it has literally been boat on boat."

The Bowen family has certainly embraced their rivalry that began when the 12-strong Clipper race fleet of 70 footers left London on August 31 for the first leg to Rio de Janeiro.

"Our cousin has a wager on us," Caroline says, adding when asked what is to be gained or lost: "a life time of humiliation" – no doubt for who is beaten by the other.

The pair are now readying themselves for Saturday's start of the Sydney to Hobart that could be one of the potentially toughest legs, even though it is a relatively short one at 628 nautical miles.

Asked about their sibling competitiveness, the two regular sailors don't shroud it in denial.

Notwithstanding, their last leg, 2,088 nautical miles from Albany in Western Australia to Sydney, was a belter.

However, who 'wins' the contest between them will be known sooner than later.

Caroline is racing the full Clipper race to its finish back in London, whereas Leo will return to England after leg six from Hobart to Airlie Beach in Queensland due to her work commitments as a doctor.

The pair clearly recall how they came to sign up for the Clipper race that is held every two years - the first time in 1996, and the last before this year's edition in 2013 when it also incorporated the Sydney to Hobart.

The brainchild of British ocean racing great, Sir Robin Knox-Johnston, the 40,082 nautical mile is also the only global race open for amateur sailors who are assigned to boats skippered by professional sailors.

The Bowen sisters are nonetheless seasoned sailors, and it was during the Cowes Week regatta in England in August - just before the Clipper Race - that they opted to sign up.

"I was just sailing back [at Cowes] one afternoon and thought, 'Maybe it is the right time ...," Caroline says.

"It was quite short notice and thought, 'I've got no reason not to do this.' That evening I said to Leo, 'C'mon ... this is the right time to do it.

"And it was. We were both able to take time out of our careers right now.

"So it is fantastic to share this with her because as Leo said we have always sailed in different fleets and very rarely have sailed against together.

"We are not the sort of siblings that have done these things together, so it's amazing."

Rosalind Bowen is spending Christmas in Sydney with her daughters and will be seeing them start the Race on Boxing Day 26th December.